[Tropical] Tropical Cyclone Discussion

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WTNT42 KNHC 030245
TCDAT2

Tropical Storm Philippe Discussion Number  39
NWS National Hurricane Center Miami FL       AL172023
1100 PM AST Mon Oct 02 2023

Philippe continues to be under the influence of significant
westerly to northwesterly vertical wind shear.  The center, which
is located on the northwestern edge of the main area of deep
convection, recently passed over Barbuda.  Most of the stronger
convection is over the southern and southeastern portions of the
circulation, so the Leeward Islands should continue to experience
strong winds and heavy rains even when the center of the storm
begins to move north of those islands.  The current intensity is
kept at 45 kt based on SFMR-observed surface winds from an Air Force
Hurricane Hunter aircraft that is still investigating the system.

The cyclone has wobbled west-northwestward this evening and the
current motion estimate is 300/6 kt.  Over the next few days,
Philippe should move along the western periphery of a mid-level
subtropical high pressure area.  Most of the guidance model tracks
have shifted even farther west, with the exception of the GFS
deterministic and ensemble mean forecasts, which appear to be
eastern outliers at this time.   Based the new dynamical model
consensus, the official forecast track is, again, shifted farther
west from the previous one.  Later in the forecast period, the
spread in the guidance models increases.  Notably,the GFS
prediction shows that a mid-tropospheric trough over the
northwestern Atlantic fails to capture the cyclone and take it
northward into Atlantic Canada, but keeps Philippe moving slowly
over the subtropical Atlantic at 5 days and even beyond.

Little change in intensity is likely for the next couple of days
while the storm remains in an environment of strong vertical wind
shear.  In 2 to 3 days, the global models suggest that Philippe
could encounter a more favorable upper-tropospheric wind
environment, with more anticyclonic and diffluent upper-level winds
evolving over the system.  Therefore, some strengthening is
predicted in the latter half of the forecast period.  The official
intensity forecast is near the high end of the model guidance,
however.


KEY MESSAGES:

1. Tropical storm conditions are expected across Barbuda and
Antigua tonight while Philippe passes just north of the area.
Interests elsewhere in the northern Leeward Islands should continue
to monitor this system.

2. Heavy rainfall from Philippe is expected to produce scattered
flash flooding across portions of the Leeward and northern Windward
Islands, particularly between Barbuda and Dominica, into early
Wednesday.


FORECAST POSITIONS AND MAX WINDS

INIT  03/0300Z 17.8N  62.1W   45 KT  50 MPH
 12H  03/1200Z 18.4N  62.8W   45 KT  50 MPH
 24H  04/0000Z 19.7N  63.4W   45 KT  50 MPH
 36H  04/1200Z 21.3N  64.0W   45 KT  50 MPH
 48H  05/0000Z 23.0N  64.4W   45 KT  50 MPH
 60H  05/1200Z 24.8N  64.7W   50 KT  60 MPH
 72H  06/0000Z 26.9N  64.3W   55 KT  65 MPH
 96H  07/0000Z 31.6N  62.8W   60 KT  70 MPH
120H  08/0000Z 36.0N  60.0W   60 KT  70 MPH

$$
Forecaster Pasch
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